George Julius Poulett Scrope, (born March 10, 1797, London—died Jan. 19, 1876, Fairlawn, Surrey, Eng.) English geologist and political economist whose volcanic studies helped depose the Neptunist theory that all the world’s rocks were formed by sedimentation from the oceans. Originally surnamed Thomson, he assumed the surname Scrope in 1821 on his marriage to the daughter of William Scrope, the last of the old earls of Wiltshire.

George Julius Poulett Scrope, engraving, 1875.

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As an undergraduate he visited Naples in 1816–17, where his interest in volcanoes was stimulated by the activity of Vesuvius. In 1821 he examined the extinct volcanoes of the Auvergne, in central France, and collected material for his On the Geology and Extinct Volcanoes of Central France (1827).

Scrope began his studies when the doctrines of German geologist Abraham G. Werner were still predominant, but he was soon to play a part in the overthrow of Werner’s Neptunist ideas. His first work, Considerations on Volcanoes (1825), is regarded as the earliest systematic treatise on volcanology, since it was the first attempt to frame a satisfactory theory of volcanic action and to show the part volcanoes have played in the Earth’s history. He early appreciated the important part played by water in volcanic action, and he disposed of the theory that craters are formed by the buckling of the Earth’s crust.

Soon after his marriage, Scrope settled at the family seat of Castle Combe, Wiltshire, and devoted his attention largely to social and political questions. He was a member of Parliament from 1833 until 1868 and published a long series of pamphlets and reviews advocating free trade and social reforms.